On a molecular level, the body functions with an enormously complex set of chemical reactions. These chemical reactions require energy, which is where calories step in.

Bottom Line: A dietary Calorie is the amount of energy required to heat 1 kilogram of water by 1 degree Celsius. The body uses energy (calories) to drive chemical reactions.

What Does Calories in, Calories Out (CICO) Entail?

According to the “calories in, calories out” (CICO) way of thinking, obesity is simply a matter of eating too many calories.

Proponents of this often say that the types of foods you eat aren’t very important, that the caloric contribution of foods is the key.

They say that the only way to lose weight is to eat less, move more and that it is any individual’s responsibility to keep calories balanced.

A pound of fat is 3500 calories (a kilogram is 7700). If you eat 500 calories less than you burn every day, then after a week (7 * 500 = 3500) you will have lost a pound of fat.

From this comes “a calorie is a calorie” the idea that all calories are created equal, no matter what foods they come from.

Even though it is true that obesity is caused by excess calories and weight loss caused by a calorie deficit, this is still such a drastic oversimplification that it is downright wrong.

Different Foods Affect Our Hormones in Different Ways

In my opinion, one of the biggest fallacies in nutrition is to think that all calories are created equal.

Different macronutrients (proteins, fats and carbohydrates) go through different metabolic pathways.

Let me show you this with two examples – fructose and protein.

Fructose

Fructose, when it enters the liver from the digestive tract, can be turned into glucose and stored as glycogen.

But if the liver is full of glycogen, it can be turned into fat which is then shipped out or lodges in the liver.

Consumed in excess, it can cause insulin resistance, which raises insulin levels all over the body. Insulin drives fat gain (2, 3).

Fructose also doesn’t get registered in the same way as glucose and doesn’t impact satiety in the same way. Fructose doesn’t lower the hunger hormone ghrelin

Maybe We’ve Got Things Backwards

Most people believe that the increased calorie intake is driving the weight gain.

But what if we’ve got things backwards and the fat gain drives the increased calorie intake?

When a teenage boy grows rapidly in height, he eats more calories than he expends. Instead of turning into fat, the calories are used to build muscle, bones, skin and organs.

It is not the increased calorie intake that is driving the growth, but hormones, growth factors and physiological processes that are causing the growth and the growth drives the increased calorie intake. That makes sense, right?

What if obesity is similar? What if calories are a consequences of the weight gain, not a cause?

In the same way that a teenage boy’s muscles and bones grow because of hormones, an obese person’s fat mass may be growing because of hormones.

One example of this is drugs like some antidepressants and birth control pills, which often have weight gain as a side effect.

There are no calories in these pills, but they alter the physiology of the body (brain and hormones) to cause weight gain. In this case, the increased calorie intake is secondary to the change in hormones.

Bottom Line: It is possible that we are confusing cause and effect. Perhaps it’s not the increased calorie intake that drives the fat gain, but the fat gain that drives the increased calorie intake.

Eating Behavior is Largely Subconscious

Humans aren’t robots.

We don’t walk around and make decisions about our behavior based on mathematical calculations. It is against our nature.

We make decisions based on our emotions, how we feel and what we want to do. The “logical” part of our brain often doesn’t have much control over the part of our brain that is regulated by emotions.

Some might call this weakness, I call it human nature. Changing behavior based on logical, rational decisions can often be impossible.

Ever made a decision not to drink coffee after 2pm? Always do homework right after school? Only sleep in on Sundays?

Making these kinds of changes in your life is often very difficult and the same applies to eating behavior like making the decision to eat 500 calories below your maintenance every day.

Even though some highly motivated individuals are able to control their food intake completely (like athletes and bodybuilders), this really isn’t representative of the general population.

This is very difficult for most people and especially for people who have a tendency to gain weight.

Let me use breathing as an example of how it is difficult to “control” a physiological function that is regulated by the brain.

Breathing is almost completely subconscious, although you can control your breathing for a short amount of time if you manage to focus on it.

If you made the decision to skip 1 in 10 breaths, then you could probably do it, but only for a few minutes. Then you’d get distracted and start doing something else.

This is only possible while you’re consciously focusing on it and even if you did, you might unwillingly compensate by breathing a little heavier in the other 9 breaths, or you’d start to feel uncomfortable and stop doing it altogether.

If you think this is a ridiculous example and not applicable to eating, then you’re wrong. Eating is controlled with the same types of homeostatic mechanisms.

Some people may be able to consciously eat less calories and manage it with portion control and / or calorie counting. But they have to stick with it for life.

Bottom Line: Eating behavior is largely subconscious, controlled by hormones and neural circuits. It can be downright impossible to control these sorts of behaviors in the long term.